"He held a summer holiday job cleaning at the Parliament for one month in 2009 and one month in 2010. Those were the only instances he worked at the Parliament," it said in a statement.
It did not name the individual, but a source close to the inquiry told AFP it was Najim Laachraoui.
Laachraoui and fellow suicide bomber Ibrahim El Bakraoui blew themselves up at Brussels airport in coordinated attacks two weeks ago that also struck a Brussels metro station and killed a total of 32 people.
The European Parliament said the suspect did not have a criminal record when he worked for the cleaning firm it had contracted at the time.
"As required by the contract, the cleaning firm submitted proof of the absence of a criminal record to the European Parliament," the statement said.
Laachraoui, 24, is understood to have travelled to Syria in 2013.
He resurfaced last September, two months before the Paris attacks, when he was stopped by police on the Austria-Hungary border.
